Method for operating a compressor, and compressor

ABSTRACT

The invention relates to a method for operating a compressor ( 100 ), wherein an ionic liquid (a) is used as an operating liquid, and wherein two different materials (c, d) of the compressor ( 100 ) are brought in contact with the ionic liquid (b) and form an electrochemical element. In order to partially balance a voltage (U) of the electrochemical element at the compressor ( 110 ), a counter voltage (U G ) is applied. The invention further relates to such a compressor ( 100 ).

The invention relates to a method for operating a compressor in which anionic liquid is used as the operating fluid, and to such a compressor.

PRIOR ART

Compressors are used in particular for compressing gaseous media. Forthis purpose, the medium can be displaced, for example, by means of anoperating fluid in a displacement cylinder. In this context, suchcompressors are also referred to as piston-less compressors.

An ionic liquid can be used as the operating fluid. This is then presentin particular in an actual hydraulic oil circuit and in a gas circuit.Ionic liquids have the advantage that they have no or at least nomeasurable vapor pressure. Therefore, gas can be compressed in themanner described without parts of the operating fluid remaining in thecompressed gas, as is the case with conventional operating fluids suchas hydraulic oil.

Ionic liquids are, in particular, liquid salt, which therefore forms anelectrolyte within the compressor or the compressor system. Since, as arule, different materials are used in such a compressor for differentcomponents or parts of the compressor with which the ionic liquid isalso in contact, an electrochemical element is formed. In this case, thematerial or element that is less noble in relation to theelectrochemical series is dissolved in the ionic liquid and is degradedor consumed. At another point, this material correspondinglyaccumulates. Overall, this leads to a reduced service life or runningtime of the compressor.

Against this background, the object is to provide an option forextending service life or running time of such an ionic compressor.

SUMMARY OF THE INVENTION

This object is achieved by a method for operating a compressor and acompressor having the features of the independent claims. Preferredembodiments are the subject matter of the dependent claims and thefollowing description.

Advantages of the Invention

The present invention is based on a method for operating a compressor inwhich an ionic liquid is used as the operating fluid. If such acompressor has two different materials which are brought into contactwith the ionic liquid, an electrochemical element is automaticallyformed.

Suitable ionic liquids in this case are preferably compositions whichhave one of the following substances:

-   -   a compound in accordance with formula (I)

wherein R₁ and R₂ may be, independently of one another, hydrogen or asubstituted or unsubstituted C1-C8 alkyl, in particular a substituted orunsubstituted C1-C4 alkyl, wherein the compound according to formula (I)is in particular a 1-ethyl-3-methylimidazolium.

-   -   a quaternary ammonium compound, in particular a compound of the        formula

N⁺R₄  (II),

wherein each R may be, independently of one another, a substituted orunsubstituted C1-C4 alkyl, wherein the alkyl may in particular besubstituted by OH, wherein the compound according to formula (II) is inparticular an N,N,N-trimethylethylammonium or atris(2-hydroxyethyl)-methylammonium.

The composition can likewise have a counter-ion, in particular Cl⁻.

Relevant components or parts of the compressor which may be affected inthis case are in particular cylinder heads, pipelines, pistons, valvehousings and valves. Suitable materials are, for example, iron (orsteel), aluminum and zinc.

According to the invention, it is now provided that a counter-voltage isapplied to the compressor at least for partially equalizing a voltage ofthe electrochemical element. It is particularly useful to equalize thevoltage as completely as possible, but at least, for example, 80%, inparticular 90%.

By applying such a counter-voltage, current (that is to say externalcurrent) is thus externally introduced into the compressor, and thus thedissolution of the correspondingly less noble material or element iscounteracted or even stopped. It goes without saying that such acounter-voltage can be applied not only once between two materials, butalso between additional pairs of materials when there are additionaldifferent materials. The counter-voltage can be generated by a suitablevoltage source and can be applied at suitable points in the compressoror the corresponding components or parts.

It is now conceivable to determine the level of the counter-voltage inadvance, for example based on the electrochemical series and the voltageof the relevant materials which can be derived therefrom. In the case ofaluminum (E₀=−1.66 V) and zinc (E₀=−0.76 V), a voltage of (absolute) 0.9V results, for example. In the case of zinc and iron (E₀=−0.44 V), avoltage of (absolute) 0.32 V results, for example. The counter-voltagecan then be correspondingly specified.

However, it is particularly preferred if the voltage of theelectrochemical element is measured and the counter-voltage is set basedthereon. For this purpose, a suitable measuring device can be providedwhich, for example, detects the applied voltage at suitable points ofthe various materials. This then enables a particularly precise settingor specification of the counter-voltage and thus a compensation of thevoltage caused by the electrochemical element which is as extensive aspossible. This ultimately leads to minimal wear of the materials of thecompressor and thus of the compressor as a whole.

It is also preferred for the counter-voltage to be set as part of aregulation. In this way, possible deviations during operation of thecompressor can be equalized.

A reciprocating compressor and/or a multistage compressor is preferablyused as the compressor, in particular, for example, a multistagereciprocating compressor. Such compressors are relatively simple indesign, but nevertheless benefit from the advantages of the ionic liquidas the operating fluid. In addition, screw compressors, scrollcompressors, rotary compressors, or compressors in which two-phasemixtures can be used, are suitable.

It is advantageous if a gas, in particular hydrogen, or a gas mixture iscompressed by means of the compressor. As already mentioned, the use ofthe ionic liquid yields the advantage that no residues of this liquidremain in compressed gas and thus a particularly pure, compressed gascan be obtained. This is of particular interest especially in the caseof hydrogen, since hydrogen is used, for example, for drives, inparticular with fuel cells.

The subject matter of the invention is further a compressor in which anionic liquid is provided as the operating fluid, and in which twodifferent materials of the compressor are in contact with the ionicliquid and form an electrochemical element. This is in particular aso-called an ionic compressor. In addition, a voltage source is nowprovided, with which a counter-voltage can be applied to the compressorat least for partially equalizing a voltage of the electrochemicalelement.

Preferably, a measuring device is also provided for measuring thevoltage of the electrochemical element, wherein the voltage source isconfigured to set the counter-voltage on the basis of the measuredvoltage.

It is advantageous if a control and/or regulating unit is provided forsetting and/or regulating the counter-voltage. It is also advantageousif the compressor is configured as a reciprocating compressor and/orwith multiple stages.

With regard to the detailed explanation as well as further preferredembodiments and advantages of the compressor according to the invention,reference is made to the above explanations, which are correspondinglyapplicable here, concerning the method according to the invention, whichis explained with reference to a compressor, in order to avoidrepetitions.

The invention is schematically represented in the drawing usingexemplary embodiments and will be described below with reference to thedrawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 schematically shows a compressor according to the invention in apreferred embodiment, which is suitable for carrying out a methodaccording to the invention.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 1 shows a compressor 100 according to the invention in a preferredembodiment. In this case, the compressor has five cylinders 110, 111,112, 113 and 114 and an additional chamber 150. The cylinder 110 has amovable piston 120 as well as an inlet valve 140 and an outlet valve141, wherein these two valves are each arranged in a cylinder head 130.

The additional four cylinders are of similar design, but for the sake ofclarity no reference numerals are shown here. It should also be notedthat the additional cylinders 111 to 114 are smaller than the cylinder110 in order to allow a corresponding stage-like compression. Therespective pistons can be moved, for example, via a suitable driveaccording to the prior art (not shown here).

A gas b, for example hydrogen, can now be introduced into the cylinder110 via an inlet 121. Gas compressed within the cylinder 110 can then bedirected into the next cylinder 111 via a pipeline 120 (or anothersuitable connection). Via additional such pipelines, the still furthercompressed gas can finally be guided into the chamber 150 and from thereout of the compressor 100 via an outlet 122. In addition, a sealableconnecting line 123 is provided from the inlet 121 to the chamber 150.The chamber 150 serves to separate the ionic liquid from the gas stream;the connecting line 123 permits a flow of liquid due to the pressuredifference between the first and last compressor stages, as a result ofwhich a targeted injection of ionic liquid into the gas stream ispossible.

In each of the cylinders 110 to 114 as well as in the chamber 150, anionic liquid a, as mentioned at the outset, is now provided as theoperating fluid. In addition to a cooling and/or lubricating effect onthe compressor, a property of this ionic liquid that no residue remainsin the gas during the compression of the gas b. As already mentioned atthe outset, this is due to the fact that an ionic liquid has no or atleast no measurable vapor pressure.

Furthermore, a measuring device 160 is now provided, by means of which,for example, a voltage U between the piston 120 and the cylinder 110 orits wall is measured in this case. If the piston 120 and the cylinder110 or its wall are made of different materials, these two materialsform an electrochemical cell with a measurable—here by means of themeasuring device 160—voltage U. For example, the cylinder 110 or itswall can be made of steel (denoted by c), whereas the piston 120 can bemade of aluminum (denoted by d). As has likewise already been mentioned,this results in one of the materials dissolving in the ionic liquid band in particular depositing on the other material.

Furthermore, a voltage source 170, which can in particular also be partof a control and/or regulating unit, is now provided. By means of thisvoltage source 170, it is now possible to apply a counter-voltage U_(G)to the compressor, in this case between the piston 120 and the cylinder110 or its wall, so that a current I_(G) flows. The counter-voltage cannow be matched as precisely as possible to the measured voltage so that,as a result, there is no or at least a significantly lower voltagebetween the corresponding components or parts of the compressor, thuspreventing or at least reducing a dissolution of the one material in theionic liquid. This correspondingly increases the service life of thecompressor 110.

It goes without saying that additional such measuring devices andvoltage sources (or control and/or regulating units) can also beprovided, namely in each case between two other components or parts withdifferent materials. In particular, the aforementioned components orparts are suitable here. Overall, the service life of the compressor 110can be significantly increased in this way.

1. Method for operating a compressor (100) in which an ionic liquid (a)is used as the operating fluid, and in which two different materials (c,d) of the compressor (100) are brought into contact with the ionicliquid (b) and form an electrochemical element, characterized in that acounter-voltage (U_(G)) is applied to the compressor (110) at least forpartially equalizing a voltage (U) of the electrochemical element. 2.Method according to claim 1, wherein the voltage (U) of theelectrochemical element is measured, and the counter-voltage (U_(G)) isset based thereon.
 3. Method according to claim 1, wherein thecounter-voltage (U_(G)) is set as part of a regulation.
 4. Methodaccording to claim 1, wherein a reciprocating compressor, a screwcompressor, a scroll compressor, a rotary compressor, a compressor inwhich a two-phase mixture can be used, and/or a multi-stage compressoris used as the compressor (100).
 5. Method according to claim 1, whereina gas (b), in particular hydrogen, or a gas mixture is compressed bymeans of the compressor.
 6. Compressor (110) in which an ionic liquid(a) is provided as the operating fluid, and in which two differentmaterials (c, d) of the compressor (100) are in contact with the ionicliquid (a) and form an electrochemical element, characterized by avoltage source (170) with which a counter-voltage (U_(G)) can be appliedto the compressor (U) at least for partially equalizing a voltage (U) ofthe electrochemical element.
 7. Compressor (100) according to claim 6,comprising a measuring device (160) for measuring the voltage (U) of theelectrochemical element, wherein the voltage source (170) is configuredto set the counter-voltage (U_(G)) based on the measured voltage (U). 8.Compressor (100) according to claim 6, comprising a control and/orregulating unit for setting and/or regulating the counter-voltage(U_(G)).
 9. Compressor (100) according to claim 6, which is configuredas a reciprocating compressor, a screw compressor, a scroll compressor,a rotary compressor, a compressor in which a two-phase mixture can beused, and/or with multiple stages.